Explain how melting points are used to identify compounds and determine purity. g\

melting points are major means of identifying pure compounds.

Explanation:

A pure compound can be identified by its melting point because, a pure compound will have a sharp melting point while an impure compound will melt over a temperature range. If presented with a pure sample of an unknown solid, its melting point can tell us what the identity of the compound. Similarly, melting point analysis can show the purity of a known solid. If the known solid has a sharp melting point, then it is pure.

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2